In order to let a conventional robot perform desired work such as assembling or machining, it is necessary that an operator teach the robot motion using an operation device such as a teaching pendant or a force sensor.
In general, a robot makes motions, surrounded by many obstacles (for example, a jig for fixing an object to be assembled or machined, or a base unit for fixing the robot) which have complicated shapes and restrict its free motion. The operator teaches the robot via points to be passed through or a posture to be taken changing its posture so that the robot can avoid the obstacles.
However, the robot which merely passes through the via points accurately may make many wasteful motions, which leads to increase in cycle time of its automated operation. In order to avoid this, the operator needs to optimize the via points or motion paths of the robot through trial-and-error coordination in which the operator actually operates the robot at low speed. However, such trial-and-error coordination involves high time cost or much property damage due to a careless mistake. Such cost and damage sharply increase when the operator has little experience.
In view of this, a method has been proposed in which, during direct teaching, a robot automatically obtains a space accessible to the robot, and the robot automatically generates an optimum path for its automatic operation (for example, see NPL 1). In the method disclosed in NPL 1, a robot automatically obtains a space swept through by its body in direct teaching (hereinafter referred to as a swept space) as an accessible space, and uses the automatically obtained space as a search space within which the robot searches for an optimum path.
The term “direct teaching” means a teaching method in which an operator teaches a robot a motion by directly moving the robot using the operator's body (such as a hand). A robot which can be taught by direct teaching controls its movable part according to external force detected by a force sensor, for example.
The term “swept space” means a space through which an object has moved. In other words, a swept space is a set of spaces temporarily occupied by an object. Therefore, a swept space of a robot in direct teaching is a set of spaces where the robot has moved or stopped in the direct teaching.
FIG. 34 schematically shows conventional processing for obtaining an accessible space and processing for searching for an optimum path. According to NPL 1, an operator 201 teaches a robot 202 a motion by direct teaching using a force sensor mounted on the end of the robot 202. An accessible space 203 is calculated by combining spaces occupied by the robot 202 itself in direct teaching. Then, a motion path 204 between two points is searched for within the calculated accessible space 203. In other words, the accessible space 203 is used as a search space. The robot 202 moves along the motion path 204 determined as a result of the searching so that the robot 202 can automatically works, avoiding the obstacle.